Development and regeneration of neural components of the visual system have been the objects of intensive investigation in vivo. In vitro, aggregate cultures of neural retina have also been studied in several respects, including the increase of choline acetyltransferase (CAT) in co-aggregates of retina and optic lobe from the chick embryo. However, there is little or no description or retinal or optic tectum neurons in monolayer cultured, the availability of which could permit detailed investigations on 1) the conditions and trophic influences required for neuronal survival, 2) trophic or specifying interactions between retinal and tectal neurons, and 3) directional instructions for the guidance of elongating retinal neurons. In this project, a preliminary success in obtaining such neuronal monolayer cultures from chick embryo neural retina and optic lobe will be followed up with a detailed definition of optimal dissociation, culture, and cell purification conditions, and the characterization of the cultured neurons by morphological categorization, cholinergic competence (CAT production and choline uptake), cholinoceptive competence (alpha-bungarotoxin binding), and GABA competence (GABA accumulation). Interactions between retinal and tectal neurons will be investigated at the humoral level (cross-conditioned media, and their putative active constituents) and the cellular level (monolayer and aggregate co-cultures), by monitoring cell numbers, neurite and pattern developments, and CAT activity. Lastly, efforts will be made to develop physical model systems for the study of neurite growth and guidance. Successful models will eventually be used to investigate the interaction of neural retina and optic lobe neurons with cell-free terrains and/or glial cell populations, including neuritic behavior after in vitro transection.